score = eval(input("请输入成绩："))
if 0 <= score < 60:
    grade = "D"
    print(grade)
elif 60 <= score < 75:
    grade = "C"
    print(grade)
elif 75 <= score < 85:
    grade = "B"
    print(grade)
elif 85 <= score <= 100:
    grade = "A"
    print(grade)
else:
    print("输入错误")